A computer controlled switching stimulator/amplifier is proposed which is capable of delivering electrical stimuli between pairs of intracranial electrodes, while simultaneously monitoring the EEG potentials on all implanted electrodes immediately before and after stimulus application In phase 1, a key feasibility issue will be to study the electro-chemical effects that that leave residual potentials on the electrodes immediately after stimulation which can block viewing the EEG. The knowledge gained will be used to build a breadboard EEG amplifier-stimulus generator combination which will permit recording and observation of the EEG in the stimulated channel as soon as possible after termination of the stimulus waveform train. Phase 2 will have the specific aim of embodying the design into a marketable product capable of expansion to at least 128 channels. Two 128 channel systems will be built. The developed hardware and software will be beta tested using human subjects who would normally be scheduled for clinical functional mapping prior to resective brain surgery for epilepsy. The technology developed will also be useful for brain functional mapping preceding other resective surgery such as for tumors.